1. Field of the Invention
The present invention relates to a test instrument, and more specifically, to a power source test instrument for a circuit.
2. Description of the Prior Art
In modern society, portable electronic apparatuses, such as mobile phones, personal digital assistants (PDAs), walkmans, digital versatile disk players, hand-held computers, and notebook computers, by means of their portability, play a role for users to communicate mutually, access data, accumulate knowledge, and further raise the quality of living and work efficiency. As the size and weight of portable electronic apparatuses are reduced, it has become common to carry two or more portable apparatuses. For users” convenience, typical portable electronic apparatuses use rechargeable batteries for their power supply because a rechargeable battery can simply be recharged after use, which is more economical and environment-friendly.
Generally, common rechargeable batteries can be divided into nickel batteries and lithium batteries, and nickel batteries can be further divided into nickel—cadmium (NiCd) batteries and nickel—hydrogen (NiH) batteries. A NiCd battery uses a simple circuit, has better performance for rapid recharging, high load of current, long persistence and voltage firmness. However, a NiCd battery also has a strong memory effect which means, if the battery is not discharged before recharging, the battery stores the remaining electricity and cannot be fully recharged. Additionally, cadmium pollutes the environment. Because NiCd batteries are heavy in weight, are high polluting, and have a strong memory effect, they are gradually retiring from the market. NiH batteries are cadmium-free and reliable, meaning less polluting and more environment-friendly. Additionally, NiH batteries have a higher storage density than NiCd batteries, but as with NiCd batteries, NiH batteries also have a memory effect, however, it is less obvious.
Lithium batteries can be divided into lithium polymer batteries, lithium ion batteries, and lithium metal batteries. The lithium metal battery is the superior battery, having advantages that the two other types do not have. A lithium metal battery has high safety being safe from any physical or electrical influences, such as internal or external short, overcharge, over-discharge, or overheat. Additionally a lithium metal battery is a non-memory effect battery with its self discharge ratio at 1%–2% per month. It also has a smooth discharge curve and provides a strong current. A lithium ion battery is a high energy density battery with no memory effect and high storage, but it needs a special charger or it is incompletely discharged and short-lived. A lithium polymer battery is similar to a lithium ion battery. It is worth noting that a lithium polymer battery has the highest self discharge ratio up to 20% per month, and therefore a lithium polymer battery can be easily determined by testing this parameter.
As mentioned above, rechargeable batteries have great differences between types and, therefore, a rechargeable battery needs a special charger to properly charge the battery. For instance, a nickel battery must be discharged before being recharged but a lithium battery does not have this requirement. Additionally, a protection circuit is required to be installed in the charger to prevent over-charge or over-discharge. However, because the voltage of a battery rises when charging, it is not easy to check whether the protection circuit is in operation. Especially when chargers are mass-produced, a test instrument that does not cause damage to the charger is required. Moreover, in order to prevent over-discharge, a protection circuit is normally installed in a portable electronic apparatus and in the rechargeable battery. Consequently, a test instrument for testing whether the protection circuit works is also required.